1. Field of the Invention
The invention concerns a process for automatically regenerating copper chloride etch solutions, wherein the etchant is withdrawn from the etch chamber and regenerated in a separate regeneration unit by means of hydrogen peroxide and hydrochloric acid, diluted with water and then fed back to the etch chamber.
2. Description of the Related Art
It is known that printed circuits may be produced by etching copper and/or copper alloy coated insulation boards with a hydrochloric copper(II) chloride solution. The disadvantage of using a copper chloride solution as an etchant is, however, that such a solution becomes rapidly exhausted and has to be continually regenerated to ensure acceptable etching times. The copper(I) chloride formed when copper is etched with copper(II) chloride according to the equation EQU CuCl.sub.2 +Cu.fwdarw.2 CuCl
must be reoxidized to copper(II) chloride in the regeneration phase by adding a suitable oxidizing agent The oxidizing agents used most frequently are compressed air, which is applied through frits at the base of a stationary tank (DE-C No. 12 07 183), or chlorine gas (U.S. Pat. No. 3,083,129 and DE-C No. 16 21 437), or sodium chlorate (DE-C No. 12 25 465), or hydrogen peroxide and hydrochloric acid (DE-C No. 18 07 414 and Z. Elektronik, 1969, Vol. 11, pages 335 and 336, "Moderne Aetzverfahren fuer Druckschaltungen").
In the latter process, the aqueous solutions of hydrogen peroxide and hydrochloric acid are added within the etch system by measuring the redox potential. If there are changes in potential, the solutions are added according to DE-C No. 18 07 414 such that the first valve controlling the flow of hydrochloric acid is definitely opened before the second valve controlling the H.sub.2 O.sub.2 flow and definitely closed after the H.sub.2 O.sub.2 valve, thus ensuring that there is always an excess quantity of HCl in the solution. Put simply, during regeneration by means of the above-described oxidizing agents the following reactions occur:
Air: 2 CuCl+2 HCl+1/2 O.sub.2 .fwdarw.2 CuCl.sub.2 +H.sub.2 O PA1 Chlorination: 2 CuCl+Cl.sub.2 .fwdarw.2 CuCl.sub.2 PA1 Chlorate: 6 CuCl+NaClO.sub.3 +6 HCl.fwdarw.6 CuCl.sub.2 +3 H.sub.2 O+NaCl PA1 Peroxide: 2 CuCl+H.sub.2 O.sub.2 +2 HCl.fwdarw.2 CuCl.sub.2 +2 H.sub.2 O
According to DE-C No. 20 08 766, the exhausted etch solution may also be regenerated by means of an oxygen containing gas and by recovering the etched copper by electrolysis. Of the previously described regeneration processes, the peroxide process has so far been the most favorable for cost reasons and because of its high reaction rate and yield.
From DE-A No. 2 942 504 an etch solution containing copper(II) chloride for etching copper on circuit boards is known which in lieu of hydrochloric acid uses an alkali chloride, in particular potassium chloride, as a complexing agent. According to DE-A No. 2 942 504, the etch solution is regenerated in a simple manner by introducing air. Although this process is suitable for use on a laboratory scale, the very low reaction rate and the high air volumes needed for regeneration render it uneconomical for large-scale technical applications involving, say, &gt;1000 boards a day. Another disadvantage is that air oxidation requires that the copper(II) hydroxide thus formed, from which copper in a metallic form may be obtained by dissolution in acid and subsequent electrolysis, be filtered. This process cannot be implemented in a closed cycle, since the copper occurring as copper hydroxide is difficult to filter from the etch solution.